In　the　present　work,　lead-free　solder　balls　were　manufactured　by　a　uniform　droplet　spray　(UDS)　method.　The　solder　used　to　produce　solder　balls　was　based　on　the　Sn-3.8Ag-0.7Cu　alloy.　Different　amounts　of　cerium-based　mixed　rare-earth　(RE)　elements　were　added　into　the　Sn-3.8Ag-0.7Cu　solder　alloy　in　order　to　examine　the　effects　of　small　amounts　of　RE　additions　on　the　physical　properties,　microstructure,　and　surface　smoothness　of　the　solder　balls.　Results　show　that　a　small　amount　of　RE　addition　has　no　obvious　effect　on　the　melting　temperature,　but　it　decreases　the　nucleation　undercooling　degree.　Moreover,　a　small　amount　of　RE　addition　(＜　0.25　wt.%)　can　improve　the　surface　smoothness　of　the　solder　balls.　However,　when　the　RE　was　added　up　to　0.5　wt.%,　the　surface　smoothness　of　the　solder　balls　was　deteriorated.　From　observations　of　the　microstructure　of　the　solder　balls,　it　is　obvious　that　the　RE　addition　affects　solidification　behavior,　and　as　a　result,　the　surface　smoothness　of　the　solder　balls.